1. Field of the Invention
The present invention relates generally to dental modeling and articulating systems and methods. More particularly, the present invention relates to a hinge for such a dental modeling and articulating system.
2. Related Art
The production of a dental prosthesis requires the production of a working dental model that is a substantially exact duplication of the patient's mouth, and upon which the prosthesis can be fabricated. Such dental prostheses can include crowns, bridges, caps (substructure) for CAD/CAM production, inlays, onlays and other restorative dental works.
One method of making a dental model is referred to as the “Double Pour Method” or “pindex method.” In this method, once the model is poured and allowed time to dry, it is separated and trimmed; then holes are placed in the lower surface of the cast followed by inserting the pin with glue and placing the cast into second-pour stone base. The disadvantages of this process include: time consuming, troublesome dowel pin setup, and the requirement for two pours of casting material to create a base and a die. Moreover, this method often involves guesswork, since this method requires the technician to hand occlude two separate casts manually to set the bite. This guesswork will occasionally result in an inaccurate reproduction of the occlusal relationship of the mandibular and maxilly casts. This inaccurate reproduction will not match the original bites provided by the dentist at the time the negative impression was taken. An example of this method can be found in U.S. Pat. No. 4,734,033. This method can use a separate hinge that is separately attached to the stone bases or models. The hinge can include an adjustable ball-and-socket type connection that is rigidly fixed after the stone bases or models are aligned.
Another method is referred to as the “Single Pour Method” or “wet pinning method.” In this method, a plastic tray support member replaces the stone base mentioned above, so the second pour stage is eliminated. As a result, the whole process of making a dental model can be considerably shortened. Moreover, it is possible to mount the case without separating the upper and lower cast from the impression so that the case is mounted with the bite exactly as the impression is provided by the dentist. This “Single Pour Method” or “wet pinning technique” can include two types. The first type is the “open cavity tray type” that 1) can stabilize the prosthesis element being worked on, without shifting, or prevent movement of the prosthesis dies with the help of a notched or arcuate cavity wall which is relatively high; and 2) can eliminate the additional labor of registration pin hole drilling and the pindexing process. The disadvantages of this process include: 1) it can be difficult to control the dies over the entire process of die preparation, wax up, metal finish and porcelain build-up because there is no pin attached at the bottom of the prosthesis dies to hold to work with; 2) initial removal of the entire die from the tray can be difficult because the tray has comparatively high and notched walls necessitating the use of an extra accessory, like a special releasing device, a stand, a mallet etc., and part of the cast can break while being released from the tray; and 3) the initial stage of the wet porcelain build up can be broken because the dies can be seated firmly by a rail or spine that snap fits or clicks into the tray. Examples of such methods can be found in U.S. Pat. Nos. 5,306,145 and 6,099,305.
The second type is the “pin type”, where the plastic tray support members have plurality of registration pin holes, and the master die from this system is convenient to hold and work with since there is at least one pin protruding from underneath each segmented die. In addition, the upper cast and lower cast are not separated from the impression until they are articulated by a hinge. Thus, the case is mounted with the bite exactly as the impression provided by the dentist. One disadvantage of this process include excessive holding of the casting material stuck in the registration holes because the semi-liquid model material tends to creep through the registration holes and harden. When the model material hardens, it gets stuck in these holes, making the initial release of the segmented dies from the tray support members difficult. In addition, it may be required to break the dies off the tray forcefully, leaving tiny debris of casting material from the breakage sitting between the dies and the tray during the entire work process, interfering with the proper relationship with the adjacent dies and also the opposing model. Another disadvantage with these methods is that they often have either a flimsy hinge or separate hinges that have to be connected to the main body by harmful glue and hardening accelerator. Examples of this method can be found in U.S. Pat. Nos. 5,466,152 and 6,318,999.
Therefore, important aspects of dental modeling should include: 1) accurate, stable and easy repositioning of the sections of the model to their former relationship with the adjacent dies and also with the opposing model; and 2) the reliable registration of the upper and lower castings with respect to one another.